Just one word of warning: in general diodes and receiver front ends do not go well together, especially with SDR specimens, which have little or no narrowband preselection. If you live in an area with no strong local signals, then a diode switch could fill the bill, once it is understood that intermodulation and hence spurious signal generation are always a possibility with strong signals even far removed in frequency. In general two sub-miniature 5 V relays (at less than $ 1 apiece and drawing 70 mA each)) provide more than necessary attenuation and always deliver a "clean" signal to the RX.